Conventionally, a substance obtained by dispersing conductive substances such as carbon black, metal powder and graphite into a resin is known for a heating portion of a planar heating element.
Among other things, when a PTC (abbreviation for an English term, Positive Temperature Coefficient which means positive temperature resistance characteristics) heating element which exhibits a self-temperature control function by combining conductive substances with a resin is used, no temperature control circuit is needed, thereby reducing the number of components. Thus, such the heating element is known as an advantageous device.
As shown in FIGS. 7 and 8, on a base substrate 101 having a function as a casing structure such as ceramics and an electrically insulated metal plate, an electrode 102 obtained by printing or coating a conductive ink composition and a resistor 103 obtained by printing or coating a resistor ink composition at a position to which electricity is supplied are provided, thereby forming a heating element 104. FIG. 7 is a plan view of a heating element, and FIG. 8 is a cross-sectional view taken along line X-Y in FIG. 7.
Conventional examples in which a polymer resistor is formed by printing and is used as a heating element include an automobile door mirror for removing dew and frost, a mirror of a washing stand, a floor heating system, etc. (for example, see Patent Document 1).
Patent Document 1: JP-A-2002-371699